Add some tests for ! type

src/test/compile-fail/return-from-diverging.rs

+// Copyright 2014 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+fn fail() -> ! {
+    return "wow"; //~ ERROR mismatched types
+}
+
+fn main() {
+}
+

src/test/compile-fail/return-unit-from-diverging.rs

+// Copyright 2014 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+fn fail() -> ! {
+    return; //~ ERROR in a function whose return type is not
+}
+
+fn main() {
+}
+

src/test/run-fail/return-never-coerce.rs

+// Copyright 2014 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+// error-pattern:aah!
+
+fn call_another_fn<T, F: FnOnce() -> T>(f: F) -> T {
+    f()
+}
+
+fn wub() -> ! {
+    panic!("aah!");
+}
+
+fn main() {
+    let x: i32 = call_another_fn(wub);
+    let y: u32 = wub();
+}
+
+